This invention relates generally to current source circuitry, and more particularly to a junction field effect transistor (JFET) circuit for generating a current (I.sub.D) which is proportional to the saturation current (I.sub.DSS) of the JFET and tracks I.sub.DSS over temperature.
In an operational amplifier which utilizes JFET followers for driving a PNP differential stage, it is desirable that the JFETs be supplied each with a current equal to I.sub.DSS (the drain current when the gate and source are shorted), and in this manner provide a gate to source voltage (V.sub.gs) equal to zero and a temperature coefficient equal to zero (i.e. dVgs/dT=0). Furthermore, with V.sub.gs on both sides of the amplifier (i.e. V.sub.gs1 V.sub.gs2) equal to zero, the offset voltage V.sub.os which equals V.sub.gs1 -V.sub.gs2 would be equal to zero as would dVos/dT. Unfortunately, in the past the required current equal to I.sub.DSS of the JFET followers could not be assured sufficiency to achieve consistently acceptable results.